The global financial institution cited the "uncertainty" over the Trump administration's policies as the main reason for the downgrade.

"The major factor behind the growth revision, especially for 2018, is the assumption that fiscal policy will be less expansionary than previously assumed, given the uncertainty about the timing and nature of U.S. fiscal policy changes," the IMF said in its latest World Economic Outlook released Sunday.

The IMF also listed the U.S. economy's sluggish start to 2017 -- with a first-quarter growth of just 1.4% -- as another factor in its slashing of current forecasts.

Elsewhere around the world, meanwhile, the picture looks somewhat less grim. While the IMF also cut growth forecasts for the United Kingdom, it expects other European countries including Germany, France and Italy to grow faster in 2017 than earlier predicted. Growth forecasts for Canada, Japan and China this year were also revised up slightly.

The IMF kept its forecast for global growth unchanged at 3.5% for 2017 and 3.6% for 2018.